Too much gain - diyAudio
Go Back   Home > Forums > Amplifiers > Tubes / Valves

Tubes / Valves All about our sweet vacuum tubes :) Threads about Musical Instrument Amps of all kinds should be in the Instruments & Amps forum

Please consider donating to help us continue to serve you.

Ads on/off / Custom Title / More PMs / More album space / Advanced printing & mass image saving
Reply
 
Thread Tools Search this Thread
Old 8th September 2004, 05:23 AM   #1
miggo is offline miggo  Finland
diyAudio Member
 
Join Date: Sep 2004
Location: Finland
Question Too much gain

Hi,

I bought a "CAT SL1 improved" kit from http://www.diyclub.biz/catalog/produ...roducts_id=273 . I guess that it isn't a copy of SL1, but some ideas may be taken from there.

The problem is that the gain of this board is way too high for me since my poweramp's sensitivy is 300mV - I can't more than the first few % of volume control.

What changes would you suggest, i have tried to play with R1/R2, R10 and R11/R12 but can't guess the right values.
Lowering R2 and increasing the R1 will drop the gain, but I guess the highs are gone after that. Lowering the R10 will make the sound dull.

What would be your recommendations?

Thank you for your answers,
Attached Images
File Type: jpg sl1.jpg (19.4 KB, 942 views)
  Reply With Quote
Old 8th September 2004, 08:15 AM   #2
diyAudio Member
 
Sch3mat1c's Avatar
 
Join Date: Jan 2003
Location: Milwaukee, WI
Send a message via ICQ to Sch3mat1c Send a message via AIM to Sch3mat1c
OMG! A mu-stage with a CF after it... WTF!

Sigh... probably trying to waste tubes. Wish I could have a talk with whoever drew that... while holding a bat that is.

Anyway, a 12AU7 in place of the AX should drop a few dB... R5 and R8 will want to be more like 1k, I think.

Tim
__________________
Seven Transistor Labs
Projects and Resources
  Reply With Quote
Old 8th September 2004, 11:06 AM   #3
SY is offline SY  United States
diyAudio Moderator
 
SY's Avatar
 
Join Date: Oct 2002
Location: Chicagoland
Blog Entries: 1
With 300 mV of sensitivity, why do you even need ANY gain out of the line stage? You can lose the three tubes used in the gain stage and just run it as a cathode follower.
__________________
The more you pay for it, the less inclined you are to doubt it.- George Smiley
  Reply With Quote
Old 25th September 2004, 03:37 AM   #4
diyAudio Member
 
Join Date: Aug 2003
Location: Indiana USA
Quote:
I bought a "CAT SL1 improved" kit from http://www.diyclub.biz/catalog/prod...products_id=273 . I guess that it isn't a copy of SL1, but some ideas may be taken from there.
Same here!
I bought the same pc board several months ago!
Yes, the gain is too much. I can't solve the problem either. I simply unplugged the filament for V4!
Well, with the 6dj8 for output, the preamp sounds ok now. But....
why do I need V2 there!
C.C.
  Reply With Quote
Old 25th September 2004, 05:21 AM   #5
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Quote:
I simply unplugged the filament for V4!
That's actually the only one I would have left as is....

Cheers,
__________________
Frank
  Reply With Quote
Old 25th September 2004, 07:11 AM   #6
diyAudio Member
 
Geek's Avatar
 
Join Date: Sep 2004
Quote:
Originally posted by Sch3mat1c
OMG! A mu-stage with a CF after it... WTF!

Sigh... probably trying to waste tubes. Wish I could have a talk with whoever drew that... while holding a bat that is.
I thought that odd too Tim.

First, the audio take-off is in the wrong spot - it should be off the top tube's cathode in the mu stage and.....

They can do the stereo circuit with 3, not 4 tubes and all three 12AU7 or 12AT7 if they REALLY need gain, for simplicity and cost effectiveness.

<insert 100 rolling eyes here>
  Reply With Quote
Old 26th September 2004, 12:51 AM   #7
diyAudio Member
 
Join Date: Aug 2003
Location: Indiana USA
Default Is this circuit true??

Hi again,
I really question about this circuit, althought Lite company claimed that schematics is a copy from CAT's SL1 mk2.
It sounds ok when I cut the filament for V4. No kidding. It sounds better than my old Anthem preamp. No kidding...

C.C.
  Reply With Quote
Old 26th September 2004, 01:12 AM   #8
diyAudio Senior Member
 
fdegrove's Avatar
 
Join Date: Aug 2002
Location: Belgium
Hi,

Quote:
It sounds ok when I cut the filament for V4. No kidding.
In which case you actually take the signal straight off the cathode of the 12AU7A.
You should now have a CF with probably some signal fed back from the 12AX7A mu-follower but I'm not sure it would result in real gain. I don't think so...

Quote:
First, the audio take-off is in the wrong spot - it should be off the top tube's cathode in the mu stage and.....
If you'd want to take advantage of the properties of the mu-follower then, yes.
Since they stick a CF at the output anyway it doesn't really matter anymore anyway.

What you have now is CF in, mu-stage with a 12AX7A no less, followed by another CF...DUH...

This whole thing kind of reminds me of the Jadis linestage which is equally errr...silly.

Cheers,
__________________
Frank
  Reply With Quote
Old 2nd February 2005, 02:01 PM   #9
diyAudio Member
 
Join Date: Oct 2004
The gain is set by the feedback loop, so changing/supressing the 12ax7 won't modify it.

the problem is that the voltage accross R3 defines the bias for the 12au7.

because the current in the 12au7 is negligible , you have

Gain = R10/R3= 20 (26dB)

and 12au7 Bias = (output DC) *R3/(R3+R10) = 120V* 1/21 =5,7V


If you increase R3, you need to increase R10 (and vice versa) to maintain the bias voltage for the 12au7.

So if you want to reduce the gain, you can:

-put a divider in the output (this will also reduce the hum!): simple, cheap and very effective!
-change the input valve for another that will accept higher bias voltage (if any) and reduce R10
-bias the 12au7 input (this requires an input cap and a negative supply)
-reduce the output DC, ie the 6922 input voltage either through a divider from the mustage output (decouple the musatge from the 6922 cathode follower using a capacitor , and bias the 6922 grid at 50V with two resistors), you can then halve R10.
-use a combination of the three.
  Reply With Quote
Old 2nd February 2005, 02:57 PM   #10
Zen Mod is offline Zen Mod  Serbia
diyAudio Member
 
Zen Mod's Avatar
 
Join Date: Jan 2003
Location: ancient Batsch , behind Iron Curtain
just put that pcb in deepest drawer in your room ,then make some PTP decent construction ;
you can find it at Diyaudio or somewhere else ,but you really don't need any gain with your amp's sensitivity .
try something ala Wright's SLCF or one of FDegrove's ideas
in any case-you need just CF or AF with unity gain
__________________
my Papa is smarter than your Nelson !
clean thread; Cook Book;PSM LS Cook Book;Baby DiyA ;Mighty ZM's Bloggg;Papatreasure;Papa... by Mighty ZM
  Reply With Quote

Reply


Hide this!Advertise here!
Thread Tools Search this Thread
Search this Thread:

Advanced Search

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Similar Threads
Thread Thread Starter Forum Replies Last Post
Gain Blockwith Variable Loop Gain Bonsai Solid State 17 11th July 2008 02:40 PM
How much gain should I have? komen Chip Amps 2 26th March 2006 01:32 PM
Heretical Unity Gain line stage PLUS a little gain ? yagas Tubes / Valves 7 24th January 2006 01:30 PM
Unity Gain Operation (or low gain) Tomo Chip Amps 12 22nd January 2004 01:47 AM
Q on amp gain Andrey Solid State 1 18th June 2002 09:48 PM


New To Site? Need Help?

All times are GMT. The time now is 05:47 AM.


vBulletin Optimisation provided by vB Optimise (Pro) - vBulletin Mods & Addons Copyright © 2014 DragonByte Technologies Ltd.
Copyright 1999-2014 diyAudio

Content Relevant URLs by vBSEO 3.3.2